Hi Phil, first of all thanks for raising these issues. I believe it's very helpful for my submission.
Does that mean I have to call setjmp everytime before I call libjeg function? This way the function that calls setjmp would not have been terminated.
Your choices are:
1. setjmp() in each function (scope?) that calls into libjpeg. That's nasty because setjmp(), IIRC, is detected by the compiler and prevents some optimisations. It's relatively non-intrusive in your code though.
In my opinion this is the best option I have right now.
2. setjmp() once, and make sure that that is in a scope that contains all the calls. This means turning your code inside out, but it's not impossible because - as we've noted - you never leave a jpeg file open and return to the user code, i.e. the setjmp() can happen soon after the user calls into your code. I don't think that destructors will not be called when longjmp() "pops" the stack, so you need to be careful about what types you use.
This would turn my code into an ugly huge switch statement, with a lot of code repetition. I rather not do that.
3. (deleted - idea too horrible to share.)
Don't even wanna know. ;-)
4. Try to throw an exception from the error handler. This would be ideal, if you could be sure that the exception would propagate through the C code. I believe that gcc has an option to control that. I have a feeling that it is enabled for some libraries in Debian precisely to support this sort of thing. I know nothing about other compilers, and even on Linux it's probably not reasonable to expect that the user will use a libjpeg compiled in this way.
I agree this would be support nightmare. We all know that the user wants something workable out-of-box.
5. (Grasping at straws) run libjpeg in a co-routine, err, not sure exactly how that would work, but something about an extra stack...
I'm already drowned. Maybe someone else on this mailing list can go into more details.
6. This is what I'd really like to see: copy the libjpeg source into your project, and then do (4). You could do some other tidying-up at the same time.
This is only possible if I have someone who is willing to put the time and effort in. I don't have that right now. Leaving for loooooooong ( 2 months ) vacation soon. Also, do you know whether or not libjpeg continued? What I could see is to have a separate project that provides an "updated" libjpeg source. For such users we could provide a compiler symbol to compile optimized code. I'll keep this option in mind.
My recollection is that one of the other libraries also had a setjmp error handler, but that it could be configured to instead return error codes while libjpeg can't. Not sure if that's accurate though.
Do you mean libpng? I believe I have to update my code for png, as well. Thanks again, Christian
